1. Technical Field
The present invention relates to a failure diagnosis apparatus for an exhaust gas recirculation system of an internal combustion engine.
2. Prior Art
An art disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-115259 (1998) represents a conventional failure diagnosis apparatus of this type for an exhaust gas recirculation system. FIG. 16 is a block diagram of the functional configuration of a conventional failure diagnosis apparatus for an exhaust gas recirculation system.
Shown in the figure are an EGR valve controlling means 2703, an internal combustion engine condition parameter detecting means 2702, an internal combustion engine condition parameter estimating means 2701, an internal combustion engine condition parameter comparing means 2704 for comparing the detected and estimated internal combustion engine parameters, an EGR flow judging means 2706 for diagnosing an EGR flow on the basis of the above comparison result, and an internal combustion engine condition parameter modifying means 2705 for modifying the internal combustion engine condition parameter estimating means.
When an EGR valve opening is judged greater than a specified value by the EGR controlling means, the actual suction air pressure at that time is detected by the internal combustion engine condition parameter detecting means 2702 and a suction air pressure under the EGR not working is estimated by the internal combustion engine condition parameter estimating means 2701.
A difference in outputs between the above two means represents an EGR pressure. If this pressure is higher than the threshold searched from an atmospheric pressure table, the EGR flow is judged normal. If it is lower than the threshold, the EGR flow is judged lower and faulty.
In the above step, in order to improve the accuracy of the internal combustion engine condition parameter estimating means 2701, the estimated suction air pressure under the EGR not working is adjusted with gains so that the EGR pressure becomes zero under a condition that the EGR valve is almost fully opened.
The above-mentioned failure analysis apparatus for an exhaust gas recirculation system of an internal combustion engine considers that a discrepancy between the measured and estimated fresh air suction pipe pressures is caused by a discrepancy between gains in the fresh air pressure estimating calculation, and accordingly aims to adjust the gains so that the estimated suction pipe pressure under the EGR not working becomes equal to the measured pressure.
However, there are various factors that cause an error in an estimated suction pipe pressure in practice, including dispersion of suction/exhaust temperature, dispersion of post-exhaust-stroke cylinder residual gas pressure, dispersion of actual throttle valve opening area, and error in air-flow meter, and consequently influence on the estimated pressure is different.
For example, because the post-exhaust-stroke cylinder residual gas pressure 2801 is nearly proportional to the atmospheric pressure as shown in FIG. 17, it remains consistent even if the cylinder suction volumetric flow varies. As a result, an estimated pressure error 2803 caused by this dispersion also remains consistent irrespective of the cylinder suction volumetric flow. Besides, the influence of a measurement error of the air-flow meter appears as an error on an intake air flow dependent portion 2807 of the estimated suction pipe pressure.
For the above reasons, there has been a limitation of accuracy in correcting the estimated pressure simply by adjusting the estimated pressure with gains as in the above-mentioned known art.
There has been another problem that, if the EGR gas temperature is lower than expected like in a case that the exhaust gas recirculation system has not yet been warmed up sufficiently and therefore heat of the EGR gas is absorbed by the exhaust gas recirculation system, the EGR flow may be wrongly judged lower and faulty because the actual pressure of the EGR gas becomes lower even if the EGR mass flow is normal.
There has been another problem that, since the purge valve mounted on the suction pipe is operated under a duty control, pulses are caused in the suction pipe pressure by the incoming gas through the valve and the accuracy of diagnosis is badly affected. There remains a further problem that, if purging is stopped during the diagnosis so as to prevent the above, the purge gas discharge increases.
According to the above-mentioned known art, the suction air pressure is sampled at the time when the EGR valve opening area becomes greater than a specified value and the sampled result is judged. Because of this, the diagnosis is commenced as soon as the EGR valve opening area has reached from a fully closed state up to the specified value while the suction pipe has not yet been charged sufficiently with the EGR gas.
The measured suction pipe pressure sampled as above is a pressure at the time when the EGR gas pressure has not yet increased sufficiently. Because of this, the EGR pressure calculated from the measured suction pipe pressure and estimated fresh air pressure results in a smaller value, and consequently there remains a possibility that the EGR flow is wrongly judged lower and faulty.
Since the EGR ratio is generally specified for each operation range, different EGR pressure applies in each operating range. As a result, the normal-state minimum and faulty-state maximum EGR pressures calculated from the difference between the measured suction pipe pressure and the estimated fresh air pressure under the EGR working are also different in each operation range.
Consequently, a threshold for judging the calculated EGR pressure must be specified for each operation range. Because the above-mentioned known art does not consider this point, diagnosis is available only in a limited operation range where a similar threshold applies to the judgment.
Delay of the estimated fresh air pressure is of another problem. Generally, a system configuration in FIG. 7 is used for estimating a fresh air pressure. The estimated fresh air pressure is calculated from a suction air flow, detected by a suction air flow detecting means 902 for measuring the suction air flow of a suction pipe 206, and an engine speed. Since the detected suction air flow contains a suction pulse component, a filtering process is needed to eliminate it.
Since the filtered suction air flow includes a delay as compared to the actual suction air flow, the estimated fresh air pressure 1302 calculated from this air flow is accompanied also with a delay from the actual fresh air pressure 1301. A response delay pressure between the two is proportional to an increase of the suction air flow per unit time. Because of this, if an acceleration/deceleration condition varies at time 1303, a response delay also varies accordingly.
As a result, the EGR pressure calculated by deducting the estimated fresh air pressure 1302 from the measured pressure 1307 contains an error 1311 dependent upon the operating condition. This error causes a problem that, even if the estimated fresh air pressure is corrected by an internal combustion engine parameter modifying means 2705, the estimated value shifts as the operating condition varies.
An object of the present invention is to provide a failure diagnosis apparatus for an exhaust gas recirculation system which is capable of eliminating the influence of various disturbance factors that vary the suction air pressure, diagnosing a failure of the exhaust gas recirculation system on the basis of the suction air pressure, and preventing wrong diagnosis.
In order to achieve the above objective, a failure diagnosis apparatus for an exhaust gas recirculation system of the present invention has a characteristic feature that the apparatus consists of a fresh air pressure estimating means for calculating an estimated fresh air pressure inside a suction pipe from the operating condition detected of an internal combustion engine, an actual EGR (exhaust gas recirculation) gas pressure estimating means for estimating an EGR gas pressure on the basis of a measured suction pipe pressure detected by the suction pipe pressure detecting means and an estimated fresh air pressure calculated above, and a failure judging means for judging the failure on the basis of the estimated EGR gas pressure and the detected operating condition.
To be more concrete, the present invention provides an apparatus as follows:
The present invention provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising a fresh air pressure estimating means for calculating an estimated fresh air pressure inside the suction pipe from the operating condition detected by the operating condition detecting means; an actual EGR (exhaust gas recirculation) gas pressure estimating means for estimating an EGR gas pressure on the basis of a measured suction pipe pressure detected by the suction pipe pressure detecting means and an estimated fresh air pressure calculated as above; and a failure judging means for judging the failure on the basis of the estimated EGR gas pressure and the detected operating condition.
Preferably, the apparatus comprises an estimated fresh air pressure correcting means for correcting parameters of the fresh air pressure estimating means so that the estimated fresh air becomes consistent with the measured suction pipe pressure when the EGR is not working.
Preferably, the fresh air pressure estimating means calculates the estimated fresh air pressure on the basis of, at least, an engine intake air flow parameter and an engine speed parameter from among the operating condition parameters detected by the operating condition detecting means.
Preferably, the detected operating condition includes an opening area of, at least, one or more of the multiple valves controlling the gas flow into the suction pipe, and the fresh air pressure estimating means calculates the estimated fresh air pressure on the basis of the opening area and the engine speed detected by the operating condition detecting means.
Preferably, the apparatus comprises a cylinder suction air flow calculating means for calculating a cylinder suction air flow from the detected engine suction air flow, and the parameter corrected above is a factor applicable to conversion from the calculated air flow into pressure.
Preferably, the apparatus comprises a cylinder suction air flow calculating means for calculating a cylinder suction air flow from the detected engine suction air flow, and the parameter corrected above is an offset value applicable to conversion from the calculated air flow into pressure.
Preferably, the apparatus comprises a cylinder suction air flow calculating means for calculating a cylinder suction air flow from the detected engine suction air flow, and the parameter corrected above are a factor and an offset value applicable to conversion from the calculated air flow into pressure.
Preferably, the parameter corrected above is a sum of the opening area of one or more of the valves, excluding EGR valve, controlling the air flow into the suction pipe.
Preferably, the apparatus comprises an atmospheric pressure detecting means for detecting the atmospheric pressure, and compensates the estimated fresh air pressure by the detected atmospheric pressure.
Preferably, the apparatus comprises an EGR gas pressure estimating means for estimating the pressure of the EGR gas, which is caused inside the suction pipe when an actual EGR ratio is equal to the target EGR ratio, on the basis of a target EGR ratio in a controlling means of the exhaust gas recirculation system and the estimated fresh air pressure, and the failure judging means judges the failure on the basis of the estimated actual EGR gas pressure and the estimated EGR gas pressure.
Preferably, the apparatus comprises an estimated pressure thermal compensating means for compensating, at least, either one of the estimated fresh air pressure and estimated EGR gas pressure by an estimated suction pipe gas temperature.
Preferably, calculation of the estimated suction pipe gas temperature is based on, at least, the EGR gas temperature and target EGR ratio from among the operating condition parameters detected by the operating condition detecting means.
Preferably, calculation of the estimated suction pipe gas temperature is based on, at least, the EGR gas temperature, outside temperature and target EGR ratio from among the operating condition parameters detected by the operating condition detecting means.
Preferably, a dynamic EGR ratio, which is estimated by compensating the target EGR ratio in terms of EGR gas suction pipe charging delay, is used instead of the target EGR ratio.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine; comprising a determinant value calculating means for calculating a determinant value for judging the failure on the basis of the suction pipe pressure, wherein a threshold for making a failure judgment from the determinant value is specified corresponding to, at least, either one of the engine suction air flow and engine speed detected by the operating condition detecting means.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising a diagnosis execution condition judging means for commencing the diagnosis on condition that the variation of, at least, one or more parameters influencing the gas flow inside the suction pipe from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation within a specified time of, at least, a throttle valve opening parameter from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation of, at least, a change speed parameter of the throttle valve opening from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation of, at least, an engine speed parameter from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation of, at least, a change speed parameter of the engine speed from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation of, at least, a cylinder suction air flow parameter from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
Preferably, the diagnosis is commenced on condition that the variation of, at least, a change speed parameter of the cylinder suction air flow from among the parameters detected by the operating condition detecting means is lower than a specified value and that the condition with lower variation than the specified value has continued for a specified length of time.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising an exhaust gas recirculation system temperature judging means for judging whether the exhaust gas recirculation system temperature is higher than a specified value or not, and a diagnosis execution condition judging means for commencing the execution on condition that the temperature is judged higher than a specified value.
Preferably, the apparatus comprises an EGR gas temperature detecting means for detecting the temperature of EGR gas flowing inside the exhaust gas recirculation system; and a detected EGR gas temperature judging means, instead of the exhaust gas recirculation system temperature judging means, for judging whether the EGR gas temperature detected by the EGR gas temperature detecting means is higher than a specified value or not.
Preferably, the apparatus comprises, instead of the EGR gas temperature detecting means, an EGR gas temperature estimating means for estimating the EGR gas temperature corresponding to any one of engine speed, cylinder suction air flow, ignition timing and outside temperature parameters from among the parameters detected by the operating condition detecting means.
Preferably, the exhaust gas recirculation system temperature judging means judges whether an estimated total EGR gas heating value, obtained on the basis of the target EGR ratio in the controlling means of the exhaust gas recirculation system and the engine suction air flow detected by the operating condition detecting means, is higher than a specified value, and the estimated total EGR gas heating value is compensated corresponding to either the ignition timing or the outside temperature detected by the operating condition detecting means.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising an EGR gas temperature judging means for prohibiting diagnosis on condition that, at least, one or more judgment parameters influencing the EGR gas temperature from among the parameters detected by the operating condition detecting means is outside a specified range.
Preferably, at least, suction air temperature is included in the judgment parameters.
Preferably, at least, atmospheric pressure is included in the judgment parameters.
Preferably, at least, ignition timing is included in the judgment parameters.
Preferably, at least, water temperature is included in the judgment parameters.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising a dynamic EGR ratio calculating means for calculating an estimated dynamic EGR ratio by compensating the target EGR ratio in the exhaust gas recirculation system in terms of suction pipe charging delay; and a dynamic EGR ratio judging means for comparing a difference between the estimated dynamic EGR ratio and the target EGR ratio and prohibiting diagnosis if the absolute difference between the estimated dynamic EGR ratio and the target EGR ratio is higher than a specified value.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising a failure detecting means for executing diagnosis multiple times, and determining the diagnostic result as failure when the number of failure judgments has reached a specified number or determining the diagnostic result as normality when the number of normality judgments has reached a specified number.
The present invention also provides a failure diagnosis apparatus for an exhaust gas recirculation system, which, equipped with a suction pipe pressure detecting means for detecting the suction pipe pressure of an internal combustion engine and an operating condition detecting means for detecting the operating condition of the internal combustion engine, diagnoses a failure of the exhaust gas recirculation system of the internal combustion engine on the basis of the detected suction pipe pressure and operating condition; comprising a purge valve shutting means for shutting an evaporator purge valve and executing re-diagnosis when a failure judgment is made as a result of the diagnosis.